1. Technical Field
The present invention relates to a device for erasing data, for example, servo data stored on a magnetic disk.
2. Description of the Related Art
A typical disk device comprises a magnetic disk; a spindle motor for rotating the magnetic disk; a head for writing/reading data on/from the magnetic disk, etc. Such a disk device also has a case referred to as an enclosure case used to house the magnetic disk, the spindle motor, the head, etc. On the magnetic disk is formed a data storing layer by means of sputtering. The data storing layer consists of a magnetic thin film formed on the surface of a substrate consisting of glass or such a non-magnetic material as Al or the like. Generally, the enclosure case comprises a box-like base having an opening and a plate-like top cover for covering the opening of the base.
The disk device, after assembling the magnetic disk, the spindle motor, and other components in the base, is completed by covering the opening of the base with the top cover. After this assembling, servo data, which is position data of the magnetic disk, is written on the magnetic disk together with other necessary data. The disk device, when such servo data is written thereon, is put to various performance tests in prior to the delivery. Some disk devices are judged as defective ones in these tests. Defective disk devices are disassembled so that non-defective parts are collected and reused. Before a magnetic disk is reused, however, the servo data must be erased from the disk so as to prevent the servo data written newly on the disk from interference with the old one. And, if the servo data itself is judged to be imperfect, the servo data must also be erased. Some data is also written in the above tests and such test data must be erased from the defective disk devices.
The official gazette of Japanese Published Unexamined Patent Application No. 7-29106 discloses an effective technique for erasing such data from a magnetic disk. According to the technique, a rod provided with a permanent magnet is inserted between rotating magnetic disks, thereby erasing data from those magnetic disks. Although the method disclosed in Application No. 7-29106 is effective, it is premised here that a rod provided with a permanent magnet is inserted between magnetic disks. Consequently, when magnetic disks are loaded in the above disk device, the enclosure case of the disk device becomes an obstacle, so that the rod provided with the permanent magnet cannot be inserted between the magnetic disks. In some case, therefore, the magnetic disks are unloaded from the disk device so as to erase data therefrom. For example, imperfectly written servo data can be erased while magnetic disks are loaded in the disk device. Thus, the technique disclosed in Application No. 7-29106 cannot respond to necessary requirements.
A disk device that can erase data from magnetic disks loaded in a disk device is disclosed in International Publication WO98/49674. This disk device will be described below with reference to FIGS. 11 through 13.
As shown in FIG. 11, a data eraser 400 comprises an upper magnet fixer 402, a lower magnet fixer 404, and a linkage 406. The upper magnet fixer 402 fixes permanent magnets 412 and 414 and the lower magnet fixer 404 fixes permanent magnets 416 and 418. The permanent magnets 412 and 414 are adjoining so that their different poles attract each other. The permanent magnets 416 and 418 are also adjoining so that their different poles attract each other. The permanent magnets 412 and 416 face each other in the vertical direction while different poles are disposed on opposed surfaces of the permanent magnet 412 and the permanent magnet 416. The permanent magnets 414 and 418 also face each other in the vertical direction, but different poles are disposed on opposed surfaces of the permanent magnet 414 and the permanent magnet 418.
FIG. 12 is an explanatory view of a magnetic field formed by the data eraser 400 shown in FIG. 11. As shown in FIG. 12, the magnetic field is generated almost in the center of the data eraser 400, mainly oriented in the horizontal direction. At present, the horizontal magnetic recording method is employed for magnetic disks. In order to erase data from such a magnetic disk, therefore, a magnetic field must be applied in the direction parallel to the magnetic disk. In addition, the strength of the magnetic field must be larger than the coercive force of the magnetic disk.
FIG. 13 shows a method for erasing data stored on a magnetic disk 22 with use of the data eraser 400. In FIG. 13, the top cover is removed so as to show the movement of the components in the disk device clearly. A magnetic disk 22 is rotated at first. A spindle motor in the disk device 10 is driven to rotate the magnetic disk 22. Next, the disk device 10 is inserted into a gap between the upper and lower magnet fixers 402 and 404 of the data eraser 400. At this time, the data eraser 400 is inserted so that its side where a head slider S does not exist is inserted between both fixers 402 and 404 and the head slider S is retreated as shown with an arrow in FIG. 13. This is to block the influence of a magnetic field generated by the data eraser 400. In this state, if the magnetic disk 22 is kept rotated, a magnetic field is applied to the whole surface of the magnetic disk 22 in parallel, thereby data is erased from the magnetic disk 22.
In order to erase data stored on a magnetic disk, a magnetic field that is over the coercive force of the magnetic disk must be applied onto the magnetic disk. In recent years, the recording density of such the magnetic disk has been improved remarkably, thereby the coercive force of the magnetic disk is also increased significantly. This is why a magnetic field is required that has enough strength to erase data stored on the magnetic disk.
In some cases, a magnetic disk is unloaded from the object disk device when data is also erased from the disk. As described above, however, data is erased from a magnetic disk loaded in the disk device, of course. The disk device has a spindle motor for rotating the magnetic disk and this spindle motor has a permanent magnet. The spindle motor is disposed in the center of the rotation of the magnetic disk. Consequently, if a strong magnetic field is applied to the magnetic disk so as to erase data therefrom, the magnetic field becomes a demagnetizing field of the permanent magnetic of the spindle motor, thereby it causes the characteristics of the spindle motor to be degraded. In order to improve the coercive force of the magnetic disk, it is just required to apply a stronger magnetic field to the magnetic disk, but this causes the characteristics of the spindle motor to further be degraded at the same time.
Under such circumstances, it is an object of the present invention to provide a data eraser that can apply a strong magnetic field to the magnetic disk while suppressing the strength of the magnetic field to be applied to the spindle motor.
The present invention provides a data eraser that erases data stored on a magnetic disk as described above. The data eraser comprises magnetic field generating means having two permanent magnets, each of which forms different poles, are disposed so that different poles adjoin on both an obverse and a reverse thereof; and a yoke disposed on a surface except either the obverse or the reverse of the magnetic field generating means. This data eraser erases data from the magnetic disk with use of a leaked magnetic flux from each of the obverse and the reverse on which different poles are adjoining. Consequently, the magnetic flux from either the obverse or reverse of the magnetic field generating means is not required originally so as to erase data. And, it is important to block such the unnecessary leaked magnetic flux that will affect the permanent magnet of the spindle motor.
To avoid such the problem, therefore, the data eraser of the present invention disposes the yoke on the surface except either the obverse or the reverse of the magnetic field generating means, thereby eliminating a magnetic flux to be leaked to the external space. Consequently, it is possible to reduce the influence of the magnetic field to be imposed on the spindle motor. In addition, the data eraser of the present invention can erase data not only from a magnetic disk loaded in a disk device, but also from a magnetic disk unloaded from the disk device. The yoke disposed on the surface except either the obverse or the reverse of the magnetic field generating means as described above may also be disposed so as to come in contact with the magnetic field generating means or so as to be separated slightly therefrom.
In the data eraser of the present invention, a pair of the magnetic field generating means should preferably be disposed so that different poles adjoin on their opposed surfaces of one magnetic field generating means with a predetermined gap therebetween and the magnetic disk is inserted in the gap, thereby applying a magnetic field to the magnetic disk. A pair of the magnetic field generating means, when disposed so that different poles of each permanent magnet face their opposed poles respectively, cause magnetic fields generated from them to repulse each other, thereby forming a magnetic field area consisting mainly of a component oriented in the direction parallel to the magnetic field generating means. Consequently, if a magnetic disk is inserted in the area in parallel to the magnetic field generating means, it is possible to erase data from the magnetic disk effectively.
Furthermore, the data eraser of the present invention may also be provided with a fixer for fixing a pair of the magnetic field generating means with a predetermined gap therebetween so that this fixer functions as the yoke described above. Concretely, the fixer is just required to be composed of a strong magnetic material. The fixer, when composed such way, will be able to suppress the leakage of the unnecessary magnetic flux to the external space.
Furthermore, the present invention provides a data eraser for erasing data stored on a magnetic disk. The data eraser comprises magnetic field generating means having two permanent magnets on both an obverse and a reverse thereof and a pole piece provided on either the obverse or reverse. Each of the permanent magnets forms different poles that are adjoining on both an obverse and a reverse of the magnetic field generating means. A magnetic field formed by a magnetic flux leaked from the obverse or reverse on which the pole piece is located erases data from the magnetic disk. In this data eraser, the pole piece has a function for aligning the magnetization vector of the magnetic field generated by the magnetic field generating means in orientation.
This alignment of the magnetization vectors to the tangent line of the magnetic disk is a requirement for erasing data from the magnetic disk. Consequently, if the magnetization vector is not aligned such way, a stronger magnetic field must be applied to the magnetic disk. And, this means that a strong magnetic field is applied to the permanent magnet of the spindle motor. On the contrary, if the magnetization vectors are aligned, the magnetic field may be weaker than that when not aligned for erasing data from the magnetic disk. Consequently, the magnetic field to be applied to the permanent magnet of the spindle motor becomes weak relatively.
In the above described data eraser, when erasing data, the magnetic field should preferably consist of a component oriented in parallel to the magnetic disk in the area where the magnetic disk is disposed.
Furthermore, in the above described data eraser, a pair of the magnetic field generating means can be disposed so that their surfaces on which different poles are adjoining are opposed to each other with a predetermined gap therebetween. And, the pole piece can be located on those opposed surfaces of a pair of the magnetic field generating means respectively.
Furthermore, the present invention provides a data eraser for erasing data stored on a magnetic disk. The data eraser includes magnetic field generating means and a fixer. The magnetic field generating means has two flat permanent magnets forming different poles respectively on an obverse and a reverse thereof so that the different poles adjoin on each of the obverse and the reverse. The fixer fixes the magnetic field generating means. Each of the two flat permanent magnets is increased in volume from the boundary between them or around the boundary towards outside.
In the above data eraser, a pair of the magnetic field generating means are disposed so that their surfaces on which different poles are adjoining are opposed to each other with a predetermined gap therebetween. And, the magnetic disk is inserted in the predetermined gap, thereby applying a magnetic field to the magnetic disk. The disk device can thus be inserted in the predetermined gap so that the center of the disk rotation is positioned at the boundary between the generators or around the boundary. Consequently, it is possible to improve the strength of the magnetic field to be applied to the magnetic disk while suppressing the strength of the magnetic field to be applied to the spindle motor of the disk device. The magnetic field in the data eraser should preferably be oriented towards the tangent line of the magnetic disk.
Furthermore, the present invention provides a data eraser for erasing data stored on a magnetic disk loaded in a disk device. The data eraser includes magnetic field generating means having two flat permanent magnets, each of which forms different poles, are disposed so that different poles adjoin on both an obverse and a reverse thereof; and a pole piece having a notch on part of itself is disposed on either the obverse or the reverse of the magnetic field generating means. The two flat permanent magnets are increased in volume from the boundary between them or around the boundary towards outside. In this data eraser, the use of the pole piece having such a notch makes the magnetization vectors to be distributed in uniform and an amount of the magnetic flux to be leaked into the external space, that is, the strength of the magnetic field to be adjusted partially.
In such the data eraser, a pair of the magnetic field generating means are disposed so that the surfaces on which different poles are adjoining are opposed to each other with a predetermined gap therebetween and the magnetic disk is inserted in the gap, thereby applying a magnetic field to the magnetic disk. While the magnetic disk is inserted in the predetermined gap, the notch of the pole piece should preferably come closer to the rim of the magnetic disk.